Gas-solid photocatalytic oxidation of environmental pollutants

Abstract

Means and methods employing gas-solid heterogenous photocatalysis ("GSHP") to counteract the widespread occurrence of groundwater and air polluted by volatile organic compounds (VOCs) such as trichloroethylene (TCE) and non-volatile organic compounds such as polychlorinated biphenyls (PCBs), and the like without creating other environmentally hostile agents. Common treatment methods such as spray tower aeration and activated carbon adsorption, both of which merely convert pollutants into alternate but equally obnoxious forms, can be augmented by the means and methods hereof to create ecologically innocuous byproducts. Heterogeneous photocatalysis allows the complete destruction of those organic water pollutants normally contained in the effluents of existing water treatment facilities. Ambient temperature ultraviolet-illuminated catalyst, such as, titanium dioxide, in the presence of moist air substantially completely destroys trichloroethylene (TCE) type-materials in a gaseous phase.

Accordingly, what is claimed is: 
     
       1. The method of removing halogenated and non-halogenated volatile and non-volatile organic contaminants from a gaseous stream comprising the steps of: mixing a gaseous oxygen bearing substance with the contaminated gaseous stream; contacting the contaminated gaseous stream and gaseous oxygen bearing substance mixture with a solid catalyst; and exposing the solid catalyst and contacted contaminated gaseous stream and gaseous oxygen bearing substance mixture to UV light having a wave length not greater than approximately 600 nm, to initiate under reaction conditions preselected to prevent formation of a liquid phase, a gas/solid photocatalytic reaction to convert said halogenated and non-halogenated organic contaminants, volatile and non-volatile, into primarily H 2  O and CO 2  and HX, where X is selected from the group consisting of chlorine, bromine and iodine. 
     
     
       2. A method according to claim 1 in which said gaseous stream is essentially humid air. 
     
     
       3. A method according to claim 1 in which said gaseous stream is water vapor. 
     
     
       4. A method according to claim 2 in which said UV light has a wave length of not greater than 450 nanometers. 
     
     
       5. A method according to claim 4 in which said UV wave length is between 300 and 400 nanometers. 
     
     
       6. A method according to claim 3 in which said UV light has a wave length of not greater than 450 nanometers. 
     
     
       7. A method of removing halogenated and non-halogenated volatile and non-volatile organic contaminants from water vapor, comprising the steps of: mixing an oxygen bearing substance with the contaminated water vapor; contacting the contaminated water vapor stream and oxygen bearing substance mixture with a solid catalyst; and exposing the solid catalyst and contacted contaminated water vapor and oxygen being substance mixture to UV light having a wave length of between 300 and 400 nanometers, to initiate under reaction conditions preselected to prevent formation of a liquid phase, a photocatalytic gas/solid reaction to convert said non-halogenated organic contaminants, volatile and non-volatile, into primarily H 2  O and CO 2 , and convert said halogenated organic compounds, volatile and non-volatile, into primarily CO 2  and HX, where X is selected from the group consisting of chlorine, bromine and iodine. 
     
     
       8. A photocatalytic reactor comprising a body portion surrounding a chamber portion and having a window defined therein for passing visible light having a wave length not greater than approximately 600 nm from outside said body portion into said chamber; a catalyst bed disposed within said chamber portion and positioned to receive hereupon said light from said window and become activated in response thereto; ingress means for introducing a contaminated gaseous stream into said chamber portion for exposure to a said activated catalytic bed; first egress means for withdrawing contaminants from said chamber portion; and second egress means for withdrawing the contaminant-free gaseous stream from said chamber portion. 
     
     
       9. A photoreactor according to claim 8 in which said light source generates light having a wave length of at least 320 but not more than 440 nanometers. 
     
     
       10. A photoreactor according to claim 8 in which said catalyst is selected from the group consisting of: titanium dioxide, zirconium oxide, antimony oxide, zinc oxide, stannic oxide, cerium oxide, tungsten oxide and ferric oxide. 
     
     
       11. A photoreactor according to claim 8 in which said body portion is formed of borosilicate glass. 
     
     
       12. A photoreactor comprising a body portion surrounding a chamber portion and having a window defined therein for passing visible light from outside said body portion into said chamber; a catalyst bed disposed within said chamber portion and positioned to receive hereupon said light from said window and become activated in response thereto; ingress means for introducing a contaminated gaseous stream into said chamber portion for exposure to a said activated catalytic bed; first egress means for withdrawing contaminants from said chamber portion; second egress means for withdrawing the contaminant-free gaseous stream from said chamber portion, said photoreactor being adapted to be connected in series with a conventional water treatment system and receive and detoxify the effluent therefrom. 
     
     
       13. A photoreactor according to claim 9 in which said catalyst is selected from the group consisting of: titanium dioxide, zirconium oxide, antimony oxide, zinc oxide, stannic oxide, cerium oxide, tungsten oxide and ferric oxide. 
     
     
       14. A photoreactor according to claim 9 in which said body portion is formed of borosilicate glass. 
     
     
       15. A photoreactor according to claim 10 in which said body portion is formed of borosilicate glass. 
     
     
       16. A photocatalytic reactor comprising a body portion surrounding a chamber portion and having a window defined therein passing visible light having a wave length of at least 320 but not more than 440 nanometers from outside said body portion into said chamber; a catalyst bed disposed within said chamber portion and positioned to receive hereupon said light from said window and become activated in response thereto; ingress means for introducing a contaminated gaseous stream into said chamber portion for exposure to said activated catalytic bed; first egress means for withdrawing contaminants from said chamber portion; second egress means for withdrawing the contaminant-free gaseous stream from said chamber portion, said photoreactor being adapted to be connected in series with a conventional water treatment system and received and detoxify the effluent therefrom. 
     
     
       17. A photoreactor according to claim 16 in which said catalyst is selected from the group consisting of: titanium dioxide, zirconium oxide, antimony oxide, zinc oxide, stannic oxide, cerium oxide, tungsten oxide and ferric oxide. 
     
     
       18. A photoreactor according to claim 17 in which said body portion is formed of borosilicate glass. 
     
     
       19. A method according to claim 1 in which said catalyst is selected from the group consisting of: titanium dioxide, zirconium oxide, antimony oxide, zinc oxide, stannic oxide, cerium oxide, tungsten oxide and ferric oxide. 
     
     
       20. The method according to claim 3 comprising the step of maintaining the partial pressure of said water vapor below the vapor pressure to prevent the condensation of water vapor. 
     
     
       21. The method according to claim 20 comprising the step of maintaining the partial pressure of said water vapor is at a pressure of from about one to about 10 torr.